.header {
  height: 100px;
  width: 1536px;
  background-color: black;
  opacity: 0.5;
  float: left;
  position: fixed;
  z-index: 3;
}
.header img {
  height: 60px;
  width: 250px;
  margin-left: 40px;
}
.header input {
  border-radius: 18px;
  outline: none;
  padding-left: 10px;
  background-color: black;
  opacity: 0.7;
  color: white;
  border: 1px white solid;
  height: 40px;
  margin-left: 900px;
  margin-top: 35px;
}
.header .submit {
  color: white;
  background-color: transparent;
  border: 1px white solid;
  width: 50px;
  height: 30px;
  margin-left: 30px;
  text-align: left;
}
.header .submit:hover {
  color: #4caf50;
}
.banner1 {
  width: 100%;
  height: 700px;
  background: url(https://www.tsinghua.edu.cn/qhdxdwzzb/img/bann.jpg) no-repeat
    top center;
  background-size: cover;
}
.banner1 h1 {
  color: white;
  font-size: 63.2px;
  text-align: center;
  padding-top: 350px;
}
.banner1 h2 {
  color: white;
  text-align: center;
  padding-top: 10px;
}
.topnav {
  position: relative;
  top: -30px;
  z-index: 1;
  width: 1200px;
  height: 87px;
  background-color: rgba(189, 19, 19, 10);
}
.topnav ul {
  margin-left: 100px;
  width: 1200px;
  height: 87px;
}
.topnav ul li {
  display: block;
  float: left;
  font-size: 20px;
  font-weight: 700;
}
.topnav ul li a {
  display: block;
  padding: 30px 30px;
  color: white;
}
.topnav ul li:hover {
  text-decoration: none;
  background-color: rgb(123, 18, 18);
}
.topnav ul li a:hover {
  text-decoration: none;
}
.banner2 {
  width: 100%;
  height: 100px;
  background-color: rgb(240, 241, 244);
  position: relative;
  top: -90px;
  z-index: 0;
  float: left;
}
.banner3 {
  width: 100%;
  height: 400px;
  margin: 0 auto;
}
.banner3 h1 {
  margin-top: -20px;
  text-align: center;
}
.banner3 h1:hover {
  color: black;
  text-decoration: none;
}
.banner3 .hr1 {
  width: 80px;
  height: 1px;
  border: solid;
  margin: 0 auto;
  margin-top: 15px;
  margin-bottom: 30px;
  color: rgb(179, 25, 25);
}
.banner3-content {
  width: 60%;
  height: 600px;
  margin: 0 auto;
}
.banner3 h3 {
  margin: 20px 0px;
}
.banner3 p {
  font-size: 18px;
  text-indent: 2em;
  line-height: 30px;
}
.foot {
  position: relative;
  top: 450px;
  width: 100%;
  height: 100px;
}
.foot1 {
  position: absolute;
  z-index: 2;
  width: 220px;
  height: 220px;
  background: url(https://www.ecut.edu.cn/_upload/tpl/06/0a/1546/template1546/images/mh1.png);
  background-size: cover;
  left: 70%;
}
.foot2 {
  position: absolute;
  left: 13%;
  top: 160px;
  width: 87%;
  height: 230px;
  background-color: rgb(189, 19, 19);
  z-index: 1;
}
.foot2 .foot2-content1 {
  width: 250px;
  height: 60px;
  background: url(../images/header.png);
  background-size: cover;
  float: left;
  margin: 60px;
  margin-bottom: 20px;
}
.foot .foot2-content2 {
  color: white;
  float: right;
  margin-top: 80px;
  margin-right: 240px;
}
.foot .foot2-hr {
  margin-top: 160px;
  margin-left: 60px;
  width: 1030px;
}
.foot p {
  margin-top: 25px;
  margin-left: 60px;
  font-size: 5px;
  color: white;
}
.foot3 {
  position: absolute;
  left: 10%;
  top: 220px;
  width: 90%;
  height: 170px;
  background-color: rgb(197, 169, 96);
  z-index: 0;
}
